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From: STCS8004%IRUCCVAX.UCC.IE@mitvma.mit.EDU
Newsgroups: comp.lang.scheme
Subject: Normal order (was Logic does not apply)
Message-ID: <9105081247.aa11819@mc.lcs.mit.edu>
Date: 8 May 91 16:58:00 GMT
Sender: daemon@athena.mit.edu (Mr Background)
Organization: The Internet
Lines: 45

In response to my question:

    ... *WHY NOT ALLOW THE USER* to specify normal evaluation
    when required?

John Gateley responds <GATELEY.91May3125853@datura.rice.edu>:

   Just out of curiosity, how would you compile the following function:
   (define foo
     (lambda (f x y z)
       (f z y x)))
   Consider (foo + 1 2 3) and (foo if else then pred)?
   The arguments to ANY application must be assumed to be passed in
   normal order unless you can prove otherwise. Is this what you really
   want?

No, and I hope that that isn't the unavoidable consequence! As I understand
your  point, when  the evaluator  encounters (foo  ... )  it will  not know
whether to evaluate the arguments or  not, since in the definition of 'foo'
there is nothing  to indicate what is to  be done. In the one  case all the
arguments to (f ...) need to be strict  and in the other not. But if, as in
Pascal, Algol 60, ... one is allowed  to specify the calling style for each
parameter at definition time is there still a problem? Thus couldn't

    (define f
       (lambda (x #!normal y)
           (... x  ... y ...)))

be compiled as though we had written

    (define f
        (lambda (x y)
           (... x ... (y) ...)))

and the decision whether or not to pass <arg2> by value or as a thunk in
(f <arg1> <arg2>) be made when checking that 'f' has been given two
arguments - whether compiling or interpreting?

Gordon Oulsnam                              stcs8004@iruccvax.ucc.hea.ie

PS to all readers:

  I will be incommunicado from 1600 GMT 91/05/08 to 91/05/23 so cannot
  respond immediately to messages *received* in that period (Digest 211
  and later) but will reply/summarize as appropriate on return.    G.O.